Absorbent products such as paper towels, industrial wipers, baby wipers, tissue, food service wipers, and the like are designed to provide several important properties. For example, the products should have good bulk characteristics and a soft feel. The products should be highly absorbent to fluids, including bodily fluids. In many cases, the products need good strength even after they become wet. Some products require a high resistance to tearing. Small changes in the structure or manufacturing processes of such products can provide a profound impact on the ultimate sensation to the user. Attempts have been made in the past to enhance and increase the physical characteristics of multi-ply tissue products.
One advantage of providing a multi-ply product as opposed to a single ply product is that different plies may provide different properties to the overall product. For example, disposable absorbent articles such as diapers may have a permeable first ply such as a liner in a diaper, an absorbent middle ply such as an absorbent core, and an impermeable outer ply such as a cover or backsheet. In contrast to diaper products, tissue products customarily have comprised two or three permeable plies of material. Some of the most popular tissue products on the market today include multiple plies for enhanced softness and thickness. For example, some of the premium tissues currently sold in the United States have three plies, all of which generally are structurally equivalent and equally permeable. That is, in many tissues multiple plies are provided which are essentially the same and are combined together to form a single multi-ply tissue. Typically, tissues in the prior art have plies that are structurally similar. However, some tissue products are known to have existed with heterogeneous (dissimilar) plies. Heterogeneous plies are used to accomplish several objectives in the tissue industry, such as, enhancement of strength without a reduction in softness. In some cases, heterogeneous plies can provide a mechanism to bury or separate potentially harsh or irritating substances into the center of the tissue, thereby preventing irritation to the user at the surface of the tissue. See, for example, U.S. Pat. No. 4,738,847 to Rothe et al. In some cases, a multi-ply structure has been used to provide an absorbent core in the center of the tissue, such as provided in U.S. Pat. No. 5,437,908 (Demura et al.).
At least one known disclosure is directed to forming a tissue product or laminate from two dissimilar paper webs. See U.S. Pat. No. 4,100,017 (Flautt, Jr.). The Flautt patent describes a web of low density, high bulk process paper united with a web of conventional paper. Variations described in the Flautt disclosure include using two paper webs having different creping characteristics to form the laminated sanitary tissue. It is quite possible that such a structure would be useful for an end product such as a paper towel.
Several recent United States patents disclose multi-ply tissues in which a ply includes relatively low density regions dispersed throughout a relatively high density continuous network. See U.S. Pat. Nos. 5,830,558; 5,906,711; and 5,919,556 each issued on behalf of inventor Steven Lee Barnholtz. The stated goal of such heterogeneous tissues is increased absorbency. Barnholtz discloses a three ply tissue structure in which a center or middle ply comprises a more dense, thinner ply. See for example FIGS. 2A and 2B of each patent. The center ply is thinner than the outer plies, and it is generally more compact and more dense than the outer plies. See U.S. Pat. No. 5,906,711; column 9, lines 28-36.
One problem with tissues having a thin, dense and compact middle ply is that such tissues tend to lack the superior softness that is desired by consumers. Further, the bulk and resiliency of tissues having a thin and dense middle ply is less than desirable. A thin, dense middle ply does not provide the smooth, bulky, resilient feel that consumers prefer in tissues of this type.
What is needed in the industry is a multi-ply paper product or tissue that is durable and soft having increased resiliency and enhanced substance in hand. Further, a tissue with a thicker middle ply, and a less dense (i.e. more bulky) middle ply is desirable. Furthermore, it is highly desirable to provide a product having multiple plies in which middle plies of the tissue are structurally or chemically enhanced to improve products functional performance, e.g. doesn't tear, shred or fall apart in use. A strong tissue that is also soft would be a substantial improvement over the art. Higher bulk, less dense and thicker middle layers provide advantages to the overall feel of tissues. Further, it would be desirable to find a way to store a substance within a tissue, and then enable release of the substance at a later time.